Protein-tyrosine kinases (PTKs), enzymes that catalyse the transfer of the γ phosphate of ATP to tyrosine residues of protein substrates, are critical components of signalling pathways that control cellular proliferation and differentiation. PTKs can be subdivided into two large families, receptor tyrosine kinases (RTKs) and non-receptor tyrosine kinases (NRTKs). RTKs span the plasma membrane and contain an extra-cellular domain, which binds ligand, and an intracellular portion, which possesses catalytic activity and regulatory sequences. Most RTKs, like the hepatocyte growth factor receptor c-met possess a single polypeptide chain and are monomeric in the absence of ligand. Ligand binding to the extracellular portion of RTKs, leads to dimerisation of monomeric receptors resulting in autophosphorylation of specific tyrosine residues in the cytoplasmic portion (for review see: Blume-Jensen, P., and Hunter, T., Nature 411 (2001) 355–365; Hubbard, S. R., et al., J. Biol. Chem. 273 (1998) 11987–11990; Zwick, E., et al., Trends Mol. Med. 8 (2002) 17–23). In general, tyrosine autophosphorylation either stimulates the intrinsic catalytic kinase activity of the receptor or generates recruitment sites for downstream signalling proteins containing phosphotyrosine-recognition domains, such as the Src homology 2 (SH2) domain or the phosphotyrosine-binding (PTB) domain.
Protein tyrosine kinases play a critical role in intracellular signal transduction pathways leading to diverse cellular responses such as proliferation, apoptosis and differentiation. Consequently these enzymes have become primary targets for the development of novel therapeutics designed to block cancer cell proliferation, metastasis, angiogenesis and promote apoptosis. The strategy that has progressed farthest in clinical development is the use of monoclonal antibodies to target growth factor receptor tyrosine kinases. The use of small molecule tyrosine kinase inhibitors however could have significant theoretical advantages over monoclonal antibodies. Small molecule inhibitors could have better tissue penetration, could have activity against intracellular targets and mutated targets and could be designed to have oral bioavailability. Several lead compounds have shown promising activity against such targets as the EGFR, the vascular endothelial cell growth factor receptor and bcr-abl.
The hepatocyte growth factor receptor c-met was first identified as an activated oncogene in an N-methyl-N′-nitrosoguanidinc treated human osteogenic sarcoma cell line (MUNG-HOS) by its ability to transform NIH 3T3 mouse fibroblasts. The receptor encoded by the c-met protooncogene (located on chromosome 7) is a two-chain protein composed of 50 kDa(α) chain disulfide linked to a 145 kda(β) chain in an αβ complex of 190 kDa. The α chain is exposed at the cell surface whilst the β chain spans the cell membrane and possesses an intracellular tyrosine kinase domain. The presence of this intracellular tyrosine kinase domain groups c-met as a member of the receptor tyrosine kinase (RTK) family of cell surface molecules.
Hepatocyte growth factor (HGF), also known as Scatter Factor (SF), is a multifunctional cytokine that elicits diverse responses in different cells and tissues. Since its initial discovery and characterisation HGF/SF has been the subject of intense research, particularly regarding its role in cancer development and progression. Much evidence now points to its role as a regulator of carcinogenesis, cancer invasion and metastasis (for review see: Herynk, M. H., and Radinsky, R., In Vivo 14 (2000) 587–596; Jiang, W., et al., Crit. Rev. Oncol. Hematol. 29 (1999) 209–248; Longati, P., et al., Curr. Drug Targets 2 (2001) 41–55; Maulik, G., et al., Cytokine Growth Factor Rev. 13 (2002) 41–59; Parr, C., and Jiang, W. G., Histol. Histopathol. 16 (2001) 251–268.
HGF/SF binds to and induces tyrosine phosphorylation of the mature c-met receptor β chain. Such events are thought to promote binding of intracellular signalling proteins containing src homology (SH) regions such as PLC-γ, Ras-GAP, PI-3 kinase pp60c-src and the GRB-2 Socs complex to the activated receptor. Each SH2-containing protein may activate a different subset of signalling phosphopeptides thus eliciting different responses within the cell.
C-met mutations have been well-described in hereditary and sporadic human papillary renal carcinomas and have been reported in ovarian cancer, childhood hepatocellular carcinoma, metastatic head and neck squamous cell carcinomas, and gastric cancer. C-met is also over-expressed in both non-small cell lung cancer and small cell lung cancer cells, in breast, colon and prostate tumors. Since c-met appears to play an important role in oncogenesis of a variety of tumors, various inhibition strategies have been employed to therapeutically target this receptor tyrosine kinase.
The usefulness of inhibiting the protein-tyrosine kinase c-met for inhibiting tumor growth and invasion has been shown in many well documented preclinical experiments (e.g.: Abounader, R., et al., J. Natl. Cancer Inst. 91 (1999) 1548–1556; Laterra, J., et al., Lab. Invest. 76 (1997) 565–577; Tomioka, D., Cancer Res. 61 (2001) 7518–7524; Wang, R., et al., J. Cell Biol. 153 (2001) 1023–1033).
WO 96/18626 describes inhibitors of tyrosine kinases and c-met kinase which are derivatives of 2-(2,6-dichlorophenyl)-4-phenyl-5-(pyridin-4yl)-1H-imidazole (examples 5, 6 and 55). However they show unfavorable cytochrome P450 interactions.
It has now been found that the compounds according to this invention avoid this disadvantage and are potent inhibitors of c-met kinase with good solubility.